It is estimated that about 100,000 genes are present in human chromosomes. The expression of these genes is controlled by a good-balanced regulation mechanism for a long term, whereby human bodies can be maintained healthy. More specifically, quantitative and qualitative disorders of the expression of the genes including for example the abnormal expression of the genes or the expression of abnormal gene products due to mutation cause a variety of diseases. If an abnormally expressed gene specific to a disease is identified, the gene and the protein encoded by the gene can be used for the diagnosis and therapeutic treatment of the disease.
The research works on the analysis of human genes are very meaningful not only for satisfying the interest from the field of basic biology but also for the development and research works of medicinal products and diagnostic agents. From such respect, the human genome projects for the elucidation of the entire nucleotide sequences of human genome are now under way worldwide.
However, even the currently top level scientific technology requires a long period of time for the elucidation of the whole structure of human genome, and therefore, a cDNA project to elucidate only the expressed genetic information has been drawing attention.
So far reported research works include, for example, reports about the determination of the partial sequences of cDNAs randomly selected from a cDNA library from human brain Science 252, 1651-1656 (1991); Nature 355, 632-634 (1992); Nature Genetics 2, 180-185 (1992); Nature Genetics 4, 256-267 (1993); Nature Genetics 4, 373-380 (1993)!, a report about the determination of the partial sequences of cDNAs randomly selected from a cDNA library from a human liver cell line Nature Genetics 2, 173-179 (1992)!, a report about the determination of the partial sequences of cDNAs randomly selected from a cDNA library of human islets of Langerhans Human Molecular Genetics 2, 1793-1798 (1993)! and a report about the determination of the partial sequences of cDNAs randomly selected from a human keratinocyte cDNA library Biochem. Biophys. Res. Communi. 202, 976-983 (1994)!, or a report about the determination of the nucleotide sequence of a cDNA randomly selected from a cDNA livrary derived from a human cultivated cell line (WO 94/03599).
Because these reports have been attained with major attention focused on the determination of the nucleotide sequences, where the structures of these randomly selected genes have been elucidated, the functions of the products of these genes have simply been anticipated on the basis of the examination of the homology between unknown genes and known genes or proteins already analyzed and registered in the data base, although the information of the structures of these genes have been brought about. Thus, these reports cannot directly provide information from the respect of such an application as the development of pharmaceutical products.